This invention relates generally to the field of closures for containers containing liquid at or above-atmospheric pressures such as containers for carbonated soft drinks, and the like, as well as non-carbonated fruit drinks, and more particularly, to an improved method for molding containers, the finish of which includes a frusto-conical sealing area the top end of the finish.
In my copending application Ser. No. 07/848,228 filed Mar. 9, 1992, there is disclosed a bottle finish of this type incorporating a frusto-conical sealing area adjacent the open mouth of the finish. This form of closure has proven to be very effective, and capable of withstanding internal pressures within the container in the order of 150 pounds per square inch, approximately three times the above internal pressures normally encountered during contemplated use.
However, such closures do require sealing surfaces which mate accurately on the closure and the finish of the container, which are substantially free of flaws which form potential sources of leakage. Particularly in the case of containers which are formed of molded glass, and in which commercial tolerances are relatively large, it has been found that leakage can occur if the sealing surface on the container finish has even the slightest flaw, due to the relative inflexibility or substantial resiliency of such surfaces.
In the case of containers or bottles formed from synthetic resinous materials, the problem relative to commercial tolerances is not as critical as with containers formed from glass. However, such containers are usually blow molded using a blank that has been previously formed as an injection molding, including the frusto-conical sealing surface at the finish portion thereof. Any flaw in such sealing surface is not normally corrected during the blow molding process.
In the case of glass containers, they are normally formed by injection molding in a multi-part mold. As is the case with synthetic resinous containers, the aligned edges of the mold parts are seldom perfectly fitting, so that the molded product usually has, on the outer surface thereof raised lines corresponding to each of the parting lines on the mold. When such lines extend into the frusto-conical sealing surface, the corresponding sealing surface on the closure is unable to form a complete seal, with resultant leakage occurring.
Glass containers do have a substantial advantage over synthetic resinous containers used in the soft drink and beer marketing areas. While synthetic resinous containers can and frequently are recycled, glass containers are inherently more sturdy and can be refilled for reuse as well. With repeated use, the outer peripheries of the containers are invariably subject to rubbing contact with similar containers resulting in a degree of abrasion which is usually harmless from the standpoint of appearance. However, containers of this type which incorporate the above-described frusto-conical sealing surface can incur damage in the sealing area during usual cleansing and refilling procedures which is not easily visually detected, but which, nevertheless, results in a recycled container which is no longer capable of maintaining an adequate seal with a corresponding cap applied after the container is refilled.